1. Field of the Invention
This invention relates to a luminescent apparatus using a thin film made of a luminescent material, and also to an electric appliance using the luminescent apparatus as a display. An organic EL display and an organic light-emitting diode (OLED) are included in the luminescent apparatus according to the present invention.
The luminescent materials which can be used for the present invention include all luminescent materials that emit light (phosphorescence and/or fluorescence) via singlet excitation or triplet excitation or both thereof.
2. Description of the Related Art
In recent years, the development of a luminescent element (hereinafter referred to as EL element) using a thin film (hereinafter referred to as EL film) made of a luminescent material capable of obtaining EL (electroluminescence) has been forwarded. A luminescent apparatus (hereinafter referred to as EL luminescent apparatus) has an EL element having a structure in which an EL film is held between an anode and a cathode. This apparatus is adapted to obtain luminescence by applying a voltage between the positive and cathode. Especially, an organic film used as an EL film is called an organic EL film.
A metal (typically, a metal of Group I or II on the periodic table) having a small work function is used as a cathode in many cases, while a conductive film (hereinafter referred to as a transparent conductive film) transparent with respect to visible light is used as an anode in many cases. Owing to such a structure, the luminescence obtained passes through the anode, and is visually recognized.
Recently, the development of an active matrix type EL luminescent apparatus adapted to control the luminescence of an EL element provided in each image element by using a TFT (thin film transistor) has been forwarded, and a prototype thereof has come to be made public. The constructions of active matrix type EL luminescent apparatuses are shown in FIGS. 9A and 9B.
Referring to FIG. 9A, a TFT 902 is formed on a substrate 901, and an anode 903 is connected to the TFT 902. An organic EL film 904 and a cathode 905 are formed on the anode 903, and an EL element 906 including the anode 903, organic EL film 904 and cathode 905 is thereby formed.
In this luminescent apparatus, the luminescence generated in the organic EL film 904 passes through the anode 903, and is emitted in the direction of an arrow in the drawing. Therefore, the TFT 902 becomes a luminescence screening object from an observer""s viewpoint, and causes an effective emission region (region in which an observer can make observation of luminescence) to be narrowed. In order to obtain a bright image when the effective emission region is narrow, it is necessary to increase an emission brightness but increasing the emission brightness results in an early deterioration of the organic EL film.
Under these circumstances, an active matrix type EL luminescent apparatus of a structure shown in FIG. 9B has been proposed. Referring to FIG. 9B, a TFT 902 is formed on a substrate 901, and a cathode 907 is connected to the TFT 902. An organic EL film 908 and an anode 909 are formed on the cathode 907, and an EL element 910 including the cathode 907, organic EL film 908 and the anode 909 are thereby formed. That is, this EL element 910 constitutes a structure directed contrariwise with respect to the EL element 906 shown in FIG. 9A.
In the luminescent apparatus of FIG. 9B, the luminescence generated theoretically in the EL film 908 passes through the anode 909, and is emitted in the direction of an arrow in the drawing. Accordingly, the TFT 901 enables the whole region, which is provided in a position which cannot be seen by an observer, and which has the electrode 907 thereon, to be used as an effective emission region.
However, the structure shown in FIG. 9B has potentially a problem that the structure is incapable of applying a uniform voltage to the anode 909. It is known that a resistance value of a transparent conductive film used generally as an anode is high as compared with that of a metallic film and can be reduced by thermally treating the transparent film. However, since the organic EL film has a low thermal resistance, a thermal treatment of over 150xc2x0 C. cannot be conducted after the organic EL film has been formed.
Therefore, when an anode (transparent conductive film) is laminated on an organic EL film, a thermal treatment cannot be conducted, so that it is difficult to form an anode of a low resistance value. That is, there is a possibility that a level of a voltage applied to the anode differs at an end portion and a central portion thereof. There is a fear that this problem causes a decrease in the quality of an image.
As mentioned above, in a luminescent apparatus including a structure using a transparent conductive film formed after the formation of an organic EL film, it is difficult to reduce the resistance of the transparent conductive film.
The present invention has been made in view of the above circumstances, and it is an object of the invention to provide a luminescent apparatus capable of displaying a bright, high-quality image, and also an electric appliance using such a luminescent apparatus as a display and capable of displaying an image of a high quality. The present invention will be described with reference to FIG. 1.
According to an aspect of the present invention, the method of manufacturing a luminescent apparatus has the step of connecting an auxiliary electrode to a transparent electrode, which is provided after the formation of an organic EL film, in parallel therewith so as to substantially reduce the resistance of the transparent electrode.
Referring to FIG. 1, a reference numeral 101 denotes an insulator, 102 an electrode including a reflecting surface, 103 an organic EL layer, and 104 an electrode (hereinafter referred to as transparent electrode) transparent or translucent with respect to the visible light. On the insulator 101, an EL element formed of the electrode 102 including a reflecting surface, organic EL layer 103, and transparent electrode 104 is formed.
The phrase xe2x80x9ctransparent with respect to the visible lightxe2x80x9d means that the visible light is transmitted with a transmission factor of 80-100%. The phrase xe2x80x9ctranslucent with respect to the visible lightxe2x80x9d means that the visible light is transmitted with a transmission factor of 50-80%. Although the transmission factor differs depending upon the thickness of a film, of course, the thickness of a film may be designed suitably so that the transmission factors be within the above-described range.
The insulator 101 may be formed of an insulating substrate or a substrate provided with an insulating film on a surface thereof as long as it can support the EL element.
The electrode 102 including a reflecting surface means a metallic electrode or an electrode formed of a lamination of a metallic electrode and a transparent electrode. That is, the electrode 102 means an electrode including a surface (reflecting surface) capable of reflecting the visible light on an outer surface or a rear surface thereof or an interface in the interior thereof.
The organic EL layer 103 used can be formed of an organic EL film or a laminated film of an organic EL film and a film of an organic material. That is, an organic EL film may be provided singly as a luminescent layer, or a layer of an organic material as a charge-injected layer or a charge carrying layer may be laminated on an organic EL layer as a luminescent layer. The inorganic materials include a material capable of being used as a charge-injected layer or a charge carrying layer, and a layer of such an inorganic material can also be used as a charge-injected layer or a charge carrying layer.
The transparent electrode 104 can be formed of an electrode of a transparent conductive film or an electrode of a metallic film (hereinafter referred to as a translucent metallic film) of 5-70 nm (typically, 10-50 nm) in thickness. The transparent conductive film can be formed of a conductive oxide film (typically, an indium oxide film, a tin oxide film, a zinc oxide film, a compound film of indium oxide and tin oxide, a compound film of indium oxide and zinc oxide), or a material obtained by adding gallium oxide to a conductive oxide film. When a transparent conductive film is used as the transparent electrode 104, its thickness is set to 10-200 nm (preferably 50-100 nm), and this enables the electrode to transmit the visible light with a transmission factor of 80-95%.
On the EL element 105 formed of the above-described structure, a seal member 106 and an auxiliary electrode 107 are provided, and the auxiliary electrode 107 is electrically connected to the transparent electrode 104 via anisotropic conductors 108. The anisotropic conductors 108 scattering on the transparent electrode 104 are preferably provided so that they are distributed over the whole surface thereof.
The seal member 106 is a substrate or a film transparent with respect to the visible light, and a glass substrate, a quartz substrate, a crystallized glass substrate, a plastic substrate, or a plastic film can be used. When a plastic substrate or a plastic film is used, it is preferable to provide an outer surface of a rear surface thereof with a protective film (preferably a carbon film, specifically a diamond-like carbon film) capable of preventing the passage of oxygen and water therethrough.
The auxiliary electrode 107 is an electrode provided auxiliarily for the purpose of reducing a resistance value of the transparent electrode 104, and can be made of an electrode formed of a transparent conductive film or an electrode formed of a translucent metallic film just as the transparent electrode 104. When the thickness of the auxiliary electrode 107 is set to 10-200 nm (preferably 50-100 nm) in the same manner as that of the transparent electrode 104, the auxiliary electrode can transmit the visible light with a transmission factor of 80-95%.
The anisotropic conductors 108 can be formed by using anisotropic conductive films. The anisotropic conductive film is a resin film in which conductive particles (typically metallic particles or carbon particles) are dispersed uniformly. According to the present invention, it is preferable that the anisotropic conductive films 108 be provided selectively by patterning them by photolithography, by an ink jet method, or a printing method. The reason resides in the low transmission factor of the anisotropic conductive film with respect to the visible light. Therefore, when the anisotropic conductors are provided over the whole surface of the transparent electrode 104, the light emitted from the organic EL layer 103 is absorbed thereinto.
In the luminescent apparatus including the above-described structures according to the present invention, the auxiliary electrode 107 functions as an electrode connected to the transparent electrode 104, which is formed of a transparent conductive film, in parallel therewith. Since the auxiliary electrode 107 is formed on the side of the seal member 106, a resistance value can be reduced to a low level without being restricted by the low thermal resistance of the organic EL film referred to in the descriptions of the related art examples. Therefore, when the present invention is put into practice, it becomes possible to apply a uniform voltage to the transparent electrode 104 and obtain an image of a high quality.